Various systems are known in the prior art for sensing objects in three dimensional space and converting information from the sensor or sensors into computer readable digital data from which the position and shape of the object can be determined. Most such systems include a light source for illuminating the object to be sensed and a sensor such as a video camera for recording an impression of the light from the light source which is reflected from the sensed object.
One known system includes a laser light source which emits a single plane of light. The system further includes a camera for recording a video image of the light from the light plane reflected from the sensed object. The light reflected from an object in response to illumination by a plane of light appears on the video image as one or more lines depending on the number of distinct surfaces. The lines may be straight or curved depending upon whether the particular surface of the object from which the light is reflected is flat or curved, respectively.
Assuming that the position in space of the camera and of the incident light plane are known, the position of every illuminated point on the object in three dimensional space can be determined by triangulation. Triangulation can be performed as follows. First, the laser light source illuminates the sensed object substantially greater than does the ambient light. Alternately, the camera may include a filter which passes only light having the wavelength of the light produced by the laser. Thus, any pixel of the video image illuminated with an intensity greater than a predetermined threshold intensity is assumed to reflect light produced by the laser light source. Likewise, all pixel elements which receive an illumination level less than the threshold intensity are assumed to not have received light reflected from the laser light source. Since the position of the camera in space is known, the light which illuminates any single pixel of the display must be reflected from a point in space which exists on a known line drawn from the camera lens center through the image point into space. The position of the light plane in space is also known and, since each and every point which is illuminated by the laser light source must exist on the known plane of the laser light, the exact position of each and every point illuminated by the laser light source can be determined trigonometrically by determining the point at which the known line (from the camera lens to the illuminated point) intersects the known plane. To obtain position information on the entire object, the plane of light can be sequentially scanned (angularly or translationally) a defined amount and the camera can record a second image of reflected light from the sensed object. The light plane can be sequentially moved and video images sequentially recorded until adequate information is obtained to determine the shape and position of the entire object. Alternately, the plane can remain stationary and the object can be moved under the light source. Such embodiments are not preferred, however, because physical scanning is required for these systems and, therefore, they cannot operate in real time.
Other systems exist in which multiple planes of light simultaneously illuminate the object. In a multi-plane system, only a single image frame of the object is recorded. In such a system, a method must be employed for differentiating (or disambiguating) those points which are illuminated by one plane of light from those points which are illuminated by another plane of light. Typically, such systems take an educated guess as to the plane which has illuminated one point of the video image and assumes that other illuminated points directly adjacent the first point in a direction parallel to the plane are also illuminated by the same plane. It is further assumed that the points on either side of the first point in a direction perpendicular to the parallel planes of light are illuminated, respectively, by the immediately adjacent planes of light from the laser light source. Of course, this latter assumption can be incorrect for irregularly shaped objects, and particularly objects with sharp corners between different surfaces. Thus, such systems are not particularly common because they are generally not accurate enough.
U.S. Pat. No. 4,335,962 issued to DiMatteo et al. discloses a three dimensional sensing system employing multiple planes of light and one or more cameras. This system is intended to be operated using a single camera, however, if additional accuracy is required, a second camera can be included. The position of various points on the sensed object is determined by a particular method described in the patent. In order for the method to lead to correct results, however, the primary camera must be positioned within a specified distance of the light source. The camera must be close enough to the light source such that the light reflected from the various light planes will appear to the camera in the same order in which they issued from the light source. Thus, the maximum depth that the sensed object may be is limited as well as the distance between the camera and the light source.
Therefore, it is an object of the present invention to provide a three dimensional sensing apparatus employing multiple patterns of light to illuminate the sensed object and multiple cameras which can be positioned arbitrarily to sense the object.
It is a further object of the present invention to provide a multi-camera, multi-plane three dimensional sensing system which can sense the position and shape of objects of any size.
It is another object of the present invention to provide a three dimensional sensing system which acquires information about a sensed object without mechanical scanning.
It is one more object of the present invention to provide a three dimensional sensing system which can essentially operate in real time.
It is yet a further object of the present invention to provide a three dimensional sensing system which rejects spurious light appearing in the video images.
It is yet another object of the present invention to provide an improved three dimensional sensing system.